1. Field of the Invention
The invention relates generally to sliding sleeve devices of the type used within a wellbore, and more particularly, the design of seals used within a sliding sleeve device.
2. Description of the Related Art
Sliding sleeve devices are used to allow selective fluid communication between a flowbore and a surrounding annulus in a wellbore. Typically, there devices are used as valves that are selectively opened and/or closed to accomplish a particular function within the wellbore. One typical use for such valves is to inject chemical inhibitors, stimulants, or the like into the annulus from the flowbore. During the production phase, sliding sleeve valves are often used to control the amount of flow of production fluid from the annulus into the flowbore. Many other uses for these devices are known in the art.
Conventional sliding sleeve devices include an outer housing with at least one lateral fluid flow port disposed therein. A sleeve member is disposed interiorly of the housing and is shiftable between first and second positions for selectively communicating and isolating the fluid communication port relative to the interior of the tool. The sleeve member may be shifted hydraulically, by use of a shifting tool, or using other techniques known in the art. Typically, sets of seals are located on one or both axial sides of the fluid flow port(s) to form a fluid seal between the sleeve member and the housing. These seals are important because they prevent leakage into or out of the valve device while the sleeve valve is closed. In many conventional valve designs, the seals are stacked sets of chevron-shaped seal members formed of thermoplastic material. An example of a conventional seal set is described in U.S. Pat. No. 5,309,993, issued to Coon et al. This patent is owned by the assignee of the present invention and is hereby incorporated by reference. The use of thermoplastic materials allows the seal members to flex and bend slightly so as to effect a better fluid seal, as is described in detail in U.S. Pat. No. 5,309,993.
Although standard thermoplastic seals work well for most applications, technology has continued to develop to allow oil drilling to occur at deeper intervals and consequently higher pressures and temperatures. Limitations on the use of sliding sleeve devices at these lower depths are imposed by the increased pressures and temperatures upon the seals. In applications where there is a high pressure differential between the interior flowbore and the surrounding annulus, opening and closing of the sleeve valve will degrade the seals. As the sleeve is shifted from a closed position to an open position, or vice versa, fluid will pass through the flow port(s) under great pressure and try to pass between the sleeve member and the outer housing. The thermoplastic seal members will become subjected to great erosional forces, and tend to wear away. After repeated use in such conditions, the seals may become useless.
Some contemporary seal designs have added a diffuser ring to the sleeve valve to help reduce the velocity of fluid passing through the flow port(s) as the sleeve member is being shifted between open and closed positions. An example of this type of diffuser ring is described in U.S. Pat. No. 5,309,993, issued to Coon et al. While the diffuser ring is useful, it does not completely solve the problem of erosion of the thermoplastic seal members.
The present invention addresses the problems of the prior art.